EP0932290A1 - Schnittstellenschaltung und Verfahren für eine Kommunikationseinrichtung - Google Patents

Schnittstellenschaltung und Verfahren für eine Kommunikationseinrichtung Download PDF

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Publication number
EP0932290A1
EP0932290A1 EP99101153A EP99101153A EP0932290A1 EP 0932290 A1 EP0932290 A1 EP 0932290A1 EP 99101153 A EP99101153 A EP 99101153A EP 99101153 A EP99101153 A EP 99101153A EP 0932290 A1 EP0932290 A1 EP 0932290A1
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EP
European Patent Office
Prior art keywords
gyrator
electrical current
current
opto
selectively
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP99101153A
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English (en)
French (fr)
Inventor
John Alexander Dunn
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Motorola Solutions UK Ltd
Original Assignee
Motorola Ltd
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Filing date
Publication date
Application filed by Motorola Ltd filed Critical Motorola Ltd
Publication of EP0932290A1 publication Critical patent/EP0932290A1/de
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/0002Modulated-carrier systems analog front ends; means for connecting modulators, demodulators or transceivers to a transmission line

Definitions

  • the present invention relates to an interface apparatus and method for a communications device capable of seizing a Public Switched Telephone Network, for example, a modem.
  • a modem line interface or Data Access Arrangement is used to isolate the circuitry of a modem from a telephone exchange.
  • a simplified form of a DAA 100 typically comprises an electronic inductor or gyrator 102 connected in parallel with a pulse-dial switch arrangement 104, and an AC circuit 106 for coupling high frequency signals to the modem and impedance matching the modem and the DAA 100 with a telephone exchange 108.
  • the gyrator 102 is also connected, in parallel, to the telephone exchange 108 (the border of which is shown by a broken line).
  • the gyrator 102 is an arrangement of circuit elements, for example, active elements, used to realise an inductance without the use of an inductor, and can include a direct current limiting facility; such an arrangement of circuit elements exhibits inductive and resistive properties.
  • An example of the gyrator 102 can be found in Microelectronic Circuits (published by CBS College Publishing, 1982) at page 30.
  • the simplified illustration merely shows for the purposes of simplicity and clarity of description, a resistive element 110 and an inductive element 112.
  • the AC circuit 106 is shown in simplified form; the AC circuit 106 possessing capacitive, resistive and inductive properties shown by a capacitive element 114, the resistive element 115 and a further inductive element 116, respectively.
  • a modem For a modem to be able to dial a telephone number corresponding to a terminating apparatus (not shown) with which communication is desired, for example, a computer connected to a telephone line via a further modem, a line must be seized. In order to seize the line, a direct current must be drawn ('going off-hook') in order to signal to the exchange 108 that the line is required. Referring to FIG. 2, the off-hook switch 105 is therefore actuated (FIG. 2a) so that the exchange 108 detects the current drawn, and thereby the request for the line. The pulse-dial switch arrangement 104 is not activated (FIG. 2b).
  • an undesirable LC resonance loop is formed by the resistive and inductive properties of the gyrator 102 and the capacitive, resistive and inductive properties of the AC circuit 106.
  • the LC resonance loop can oscillate when the off-hook switch 105 is switched to an "on" state, generating a transient (FIG. 2c and 2d) in the electrical current drawn from the exchange 108 and the corresponding voltage signal across the DAA 100.
  • the oscillation is initiated by the sudden appearance of a DC feed voltage 107 applied by the exchange 108 across the DAA 100 (hereinafter referred to as the "full line voltage") when the off-hook switch 105 is switched on.
  • the amplitude of the oscillation is dependent upon the time for which the gyrator 102 is not initially conducting.
  • the DC voltage across the DAA 100 falls to a much lower value due to the effect of the feed resistance 109 of the exchange 108.
  • the transient is unacceptable, since in order to achieve approval from various world-wide telecommunications standards authorities, and in particular to conform to European Standard TBR21, once the DAA 100 has started to draw a significant electrical current, the electrical current must stay above a predetermined value. The electrical current must not fall below the predetermined value because some telephone exchanges can confuse the transient with an attempt to pulse-dial.
  • the amplitude of the oscillation can be reduced by altering the time constant of the gyrator 102 or changing the AC characteristics of the AC circuit. However, such changes can introduce attenuation of data signals from the modem at the lower part of the bandwidth of the data signals. Additionally, if changes in the AC impedance of the DAA 100 occur, AC impedance regulations, in most countries, will be infringed.
  • the pulse-dial switch arrangement 104 is actuated so as to effectively shunt current away from the gyrator 102 and the AC circuit 106.
  • the off-hook switch 105 is then pulsed by actuating the off-hook switch 105 with regular interruptions so as to draw a higher-than-normal direct current pulses interspersed with regular interruptions; the number of pulses corresponding to digits being dialled.
  • an interface for a modem comprising means for selectively permitting an electrical current to flow to a gyrator, and means for selectively routing the electrical current, wherein the means for selectively routing the electrical current is coupled top the gyrator so as to channel the electrical current through the gyrator, thereby modifying the effective electrical impedance of the gyrator.
  • an interface for a communications device comprising a first switch for selectively permitting an electrical current to flow to a gyrator, and a second switch for selectively routing the electrical current, wherein the second switch for selectively routing the electrical current is coupled to the gyrator so as to channel the electrical current through the gyrator, thereby modifying the effective electrical impedance of the gyrator.
  • a method of limiting current for a communications device comprising selectively permitting an electrical current to flow to a gyrator, and selectively routing the electrical current so as to channel the electrical current through the gyrator, thereby modifying the effective electrical impedance of the gyrator.
  • a DAA 300 comprises a first rectified line 302 and a second rectified line 304 connected to an AC circuit (coupled to a modem circuit - both not shown) via a coupling capacitor 306.
  • the second line 304 is connected to a first terminal of a first opto-isolator 308, a second terminal of the opto-isolator 308 being connected to a cathode of a first diode 310 and a cathode of a second diode 312.
  • An anode of the first diode 310 is connected to a first exchange line 314 and an anode of the second diode 312 is connected to a second exchange line 316, the first and second exchange lines 314, 316 being connected to a ring circuit (not shown) known in the art.
  • the anode of the first diode 310 is also connected to the cathode of a third diode 318, an anode of which is connected to the first line 302.
  • the anode of the second diode 312 is also connected to a cathode of a fourth diode 320, the cathode of the fourth diode 320 being connected to the anode of the third diode 318.
  • the first, second, third and fourth diodes 310, 312, 318, 320 form a bridge rectifier 322.
  • the second line 304 is connected to a first terminal of a second opto-isolator 324, a second terminal of which is connected to a first terminal of a 200 ⁇ resistor 326.
  • a second terminal of the 200 ⁇ resistor 326 is connected to a first terminal of a 4.7 ⁇ F gyrator capacitor 328, a second terminal of a first 33K ⁇ resistor 330, a first terminal of a second 33K ⁇ resistor 332, and a base terminal of a first npn bipolar transistor 334.
  • a second terminal of the gyrator capacitor 328 and a second terminal of the second 33K ⁇ resistor 332 are connected to the first line 302.
  • a first terminal of the first 33K ⁇ resistor 330 and a collector terminal of the first transistor 334 are connected to the second line 304 and a first terminal of the coupling capacitor 306.
  • An emitter terminal of the first transistor 334 is connected to a first terminal of a first 11 ⁇ resistor 338, the second terminal of the 11 ⁇ resistor 338 being connected to a base terminal of a second npn bipolar transistor 342 and a first terminal of a second 11 ⁇ resister 340.
  • the second terminal of the second 11 ⁇ resistor 340 is connected to the first line 302.
  • a collector terminal of the second transistor 342 is connected to a first terminal of a third opto-isolator 336, a second terminal of the third opto-isolator 336 is connected to the base terminal of the first transistor 334.
  • An emitter terminal of the second transistor 342 is connected to the first line 302.
  • the first and second 33K ⁇ resistors 330, 332, the gyrator capacitor 328, the first transistor 334, the first and second 11 ⁇ resistors 338, 340, the second transistor 342 and the third opto-isolator 336 together form a gyrator 301. It should be noted that the second transistor 342 and the third opto-isolator 336, and either the first or second 11 ⁇ resister 338, 340 are not essential elements of the gyrator 301.
  • a line is seized as follows.
  • the first opto-isolator 308 and the second opto-isolator 324 are switched to a "on" state substantially at the same time, the second opto-isolator 324 being witched to an "on" state for a predetermined period of time, for example, 5 ms.
  • a direct current flows through the first opto-isolator 308 as shown in FIG. 4a.
  • a direct current pulse flows through the second opto-isolator 324 during the predetermined period of time (FIG. 4b).
  • the current flowing through the second opto-isolator 324 charges the gyrator capacitor 328 and turns-on the first transistor 334.
  • the third opto-isolator 336 is actuated at the same time as the first and second opto-isolators 308, 324, thereby permitting the second transistor 342 to operate in a current limiting capacity known in the art. Additionally, if the value of the resistor 326 is changed it is also possible to limit the current drawn when pulse-dialling (as described below).
  • a telephone number can be pulse-dialled using the above circuit by actuating the second opto-isolator 324 to generate a low impedance path through the gyrator 301.
  • the first opto-isolator 308 is then pulsed in a standard manner known to those skilled in the art, as described above.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Telephonic Communication Services (AREA)
EP99101153A 1998-01-21 1999-01-21 Schnittstellenschaltung und Verfahren für eine Kommunikationseinrichtung Withdrawn EP0932290A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9801276A GB2333653A (en) 1998-01-21 1998-01-21 Interface apparatus for a communications device
GB9801276 1998-01-21

Publications (1)

Publication Number Publication Date
EP0932290A1 true EP0932290A1 (de) 1999-07-28

Family

ID=10825651

Family Applications (1)

Application Number Title Priority Date Filing Date
EP99101153A Withdrawn EP0932290A1 (de) 1998-01-21 1999-01-21 Schnittstellenschaltung und Verfahren für eine Kommunikationseinrichtung

Country Status (2)

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EP (1) EP0932290A1 (de)
GB (1) GB2333653A (de)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4723267A (en) * 1985-06-17 1988-02-02 Octocom Systems, Inc. Telephone line interface and dialer circuitry for telecommunications equipment
EP0556544A1 (de) * 1992-02-18 1993-08-25 Martignoni Electronics Ag Schaltungsanordnung zum Anschluss eines Sprach- oder Datenterminals an eine Uebertragungsleitung
US5600715A (en) * 1996-02-28 1997-02-04 Lucent Technologies Inc. Integrated loop current detector apparatus for a PSTN modem

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4214130A (en) * 1978-03-10 1980-07-22 Teltone Corporation Signal coupler
GB8326997D0 (en) * 1983-02-10 1983-11-09 Redding R J Modems
US4465903A (en) * 1983-04-21 1984-08-14 Ixo, Inc. Electronic telephone interface circuit
GB2220820B (en) * 1988-07-13 1992-07-08 Philips Electronic Associated Telephone line loop current regulator

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4723267A (en) * 1985-06-17 1988-02-02 Octocom Systems, Inc. Telephone line interface and dialer circuitry for telecommunications equipment
EP0556544A1 (de) * 1992-02-18 1993-08-25 Martignoni Electronics Ag Schaltungsanordnung zum Anschluss eines Sprach- oder Datenterminals an eine Uebertragungsleitung
US5600715A (en) * 1996-02-28 1997-02-04 Lucent Technologies Inc. Integrated loop current detector apparatus for a PSTN modem

Also Published As

Publication number Publication date
GB2333653A (en) 1999-07-28
GB9801276D0 (en) 1998-03-18

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